mysql事件之修改事件（ALTER EVENT）、禁用事件（

本文实例讲述了mysql事件之修改事件（ALTER EVENT）、禁用事件（DISABLE）、启用事件（ENABLE）、事件重命名及数据库事件迁移操作。分享给大家供大家参考，具体如下： 我们要知道，MyS

本文实例讲述了mysql事件之修改事件（ALTER EVENT）、禁用事件（DISABLE）、启用事件（ENABLE）、事件重命名及数据库事件迁移操作。分享给大家供大家参考，具体如下：

我们要知道，MySQL允许我们更改现有事件的各种属性。如果我们要更改现有事件，可以使用ALTER EVENT语句，如下所示：

ALTER EVENT event_name
ON SCHEDULE schedule
ON COMPLETION [NOT] PRESERVE
RENAME TO new_event_name
ENABLE | DISABLE
DO
event_body

ALTER EVENT语句仅适用于存在的事件，如果我们尝试修改不存在的事件，MySQL将会发出一条错误消息，因此在更改事件之前，应先使用SHOW EVENTS语句检查事件的存在：

mysql> SHOW EVENTS FROM testdb;
+--------+---------------+----------------+-----------+----------+---------------------+----------------+----------------+--------+------+----------+------------+----------------------+----------------------+--------------------+
| Db | Name | Definer | Time zone | Type | Execute at | Interval value | Interval field | Starts | Ends | Status | Originator | character_set_client | collation_connection | Database Collation |
+--------+---------------+----------------+-----------+----------+---------------------+----------------+----------------+--------+------+----------+------------+----------------------+----------------------+--------------------+
| testdb | test_event_02 | root@localhost | SYSTEM | ONE TIME | 2017-08-03 04:24:48 | NULL | NULL | NULL | NULL | DISABLED | 0 | utf8 | utf8_general_ci | utf8_general_ci |
+--------+---------------+----------------+-----------+----------+---------------------+----------------+----------------+--------+------+----------+------------+----------------------+----------------------+--------------------+
1 row in set

创建一个每分钟将一条新记录插入到messages表中的示例事件来演示如何使用ALTER EVENT语句的各种功能：

USE testdb;
CREATE EVENT test_event_04
ON SCHEDULE EVERY 1 MINUTE
DO
INSERT INTO messages(message,created_at)
VALUES('Test ALTER EVENT statement',NOW());

我们来把事件修改为为每2分钟运行一次：

ALTER EVENT test_event_04
ON SCHEDULE EVERY 2 MINUTE;

我们还可以通过指定新的逻辑来更改事件的主体代码：

ALTER EVENT test_event_04
DO
INSERT INTO messages(message,created_at)
VALUES('Message from event',NOW());
-- 清空表中的数据
truncate messages;

修改完成后，可以等待2分钟，再次查看messages表：

mysql> SELECT * FROM messages;
+----+--------------------+---------------------+
| id | message | created_at |
+----+--------------------+---------------------+
| 1 | Message from event | 2017-08-03 04:46:47 |
| 2 | Message from event | 2017-08-03 04:48:47 |
+----+--------------------+---------------------+
2 rows in set

我们可以在ALTER EVENT语句之后使用DISABLE关键字来禁用某个事件：

ALTER EVENT test_event_04
DISABLE;

我们也可以通过使用SHOW EVENTS语句来查看事件的状态：

mysql> SHOW EVENTS FROM testdb;
+--------+---------------+----------------+-----------+-----------+---------------------+----------------+----------------+---------------------+------+----------+------------+----------------------+----------------------+--------------------+
| Db | Name | Definer | Time zone | Type | Execute at | Interval value | Interval field | Starts | Ends | Status | Originator | character_set_client | collation_connection | Database Collation |
+--------+---------------+----------------+-----------+-----------+---------------------+----------------+----------------+---------------------+------+----------+------------+----------------------+----------------------+--------------------+
| testdb | test_event_02 | root@localhost | SYSTEM | ONE TIME | 2017-08-03 04:24:48 | NULL | NULL | NULL | NULL | DISABLED | 0 | utf8 | utf8_general_ci | utf8_general_ci |
| testdb | test_event_04 | root@localhost | SYSTEM | RECURRING | NULL | 2 | MINUTE | 2017-08-03 04:44:47 | NULL | DISABLED | 0 | utf8 | utf8_general_ci | utf8_general_ci |
+--------+---------------+----------------+-----------+-----------+---------------------+----------------+----------------+---------------------+------+----------+------------+----------------------+----------------------+--------------------+
2 rows in set

我们可以在ALTER EVENT语句之后使用ENABLE关键字来启用事件：

ALTER EVENT test_event_04
ENABLE;

查看下事件状态：

mysql> SHOW EVENTS FROM testdb;
+--------+---------------+----------------+-----------+-----------+---------------------+----------------+----------------+---------------------+------+----------+------------+----------------------+----------------------+--------------------+
| Db | Name | Definer | Time zone | Type | Execute at | Interval value | Interval field | Starts | Ends | Status | Originator | character_set_client | collation_connection | Database Collation |
+--------+---------------+----------------+-----------+-----------+---------------------+----------------+----------------+---------------------+------+----------+------------+----------------------+----------------------+--------------------+
| testdb | test_event_02 | root@localhost | SYSTEM | ONE TIME | 2017-08-03 04:24:48 | NULL | NULL | NULL | NULL | DISABLED | 0 | utf8 | utf8_general_ci | utf8_general_ci |
| testdb | test_event_04 | root@localhost | SYSTEM | RECURRING | NULL | 2 | MINUTE | 2017-08-03 04:44:47 | NULL | ENABLED | 0 | utf8 | utf8_general_ci | utf8_general_ci |
+--------+---------------+----------------+-----------+-----------+---------------------+----------------+----------------+---------------------+------+----------+------------+----------------------+----------------------+--------------------+
2 rows in set

我们再来尝试使用ALTER EVENT重命名现有事件：

ALTER EVENT test_event_04
RENAME TO test_event_05;

来查看下事件状态：

mysql> SHOW EVENTS FROM testdb;
+--------+---------------+----------------+-----------+-----------+---------------------+----------------+----------------+---------------------+------+----------+------------+----------------------+----------------------+--------------------+
| Db | Name | Definer | Time zone | Type | Execute at | Interval value | Interval field | Starts | Ends | Status | Originator | character_set_client | collation_connection | Database Collation |
+--------+---------------+----------------+-----------+-----------+---------------------+----------------+----------------+---------------------+------+----------+------------+----------------------+----------------------+--------------------+
| testdb | test_event_02 | root@localhost | SYSTEM | ONE TIME | 2017-08-03 04:24:48 | NULL | NULL | NULL | NULL | DISABLED | 0 | utf8 | utf8_general_ci | utf8_general_ci |
| testdb | test_event_05 | root@localhost | SYSTEM | RECURRING | NULL | 2 | MINUTE | 2017-08-03 04:44:47 | NULL | ENABLED | 0 | utf8 | utf8_general_ci | utf8_general_ci |
+--------+---------------+----------------+-----------+-----------+---------------------+----------------+----------------+---------------------+------+----------+------------+----------------------+----------------------+--------------------+
2 rows in set

完事再来通过使用RENAME TO子句将事件从一个数据库移动到另一个数据库中：

ALTER EVENT testdb.test_event_05
RENAME TO newdb.test_event_05;

再来查看事件状态：

mysql> SHOW EVENTS FROM newdb;
+-------+---------------+----------------+-----------+-----------+------------+----------------+----------------+---------------------+------+---------+------------+----------------------+----------------------+--------------------+
| Db | Name | Definer | Time zone | Type | Execute at | Interval value | Interval field | Starts | Ends | Status | Originator | character_set_client | collation_connection | Database Collation |
+-------+---------------+----------------+-----------+-----------+------------+----------------+----------------+---------------------+------+---------+------------+----------------------+----------------------+--------------------+
| newdb | test_event_05 | root@localhost | SYSTEM | RECURRING | NULL | 2 | MINUTE | 2017-08-03 04:44:47 | NULL | ENABLED | 0 | utf8 | utf8_general_ci | utf8_general_ci |
+-------+---------------+----------------+-----------+-----------+------------+----------------+----------------+---------------------+------+---------+------------+----------------------+----------------------+--------------------+
1 row in set

好啦，本次记录就到这里了。

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希望本文所述对大家MySQL数据库计有所帮助。